a. Field of the Invention
The present invention relates to a process for improving the properties of granular detergents, which comprises treating the surface of the granular detergent obtained by the conventional methods for preparing granular detergents, for instance, spray granulating method, tumbling granulating method, piston granulating method, pressure granulating method and so forth thereby to make possible the maintenance of excellent caking preventability, fluidity and particle hardness extending over a long period of time.
B. Description of the Prior Art
The majority of the available heavy duty detergents are manufactured by the spray granulating method, tumbling granulating method, pressure granulating method and so forth. These kinds of detergents are convenient for use, but on the other hand are liable to become caked by contact with moisture in the air.
Therefore, the aforesaid detergent particles adhere to each other in high moisture conditions, and thereby are likely to undergo a blocking or caking phenomenon. Such a phenomenon has made said detergents extremely hard to handle and also has reduced their commercial value.
Granular detergents as aforesaid, which are inferior in fluidity, cause troubles when they are taken out of a storage silo or are charged into a carton, and even after charging thereof in the carton they undergo caking phenomena therein thereby to deteriorate their value as articles of commerce. Such being the case, there has been a demand for the improvement of the fluidity and caking preventability of detergent particles.
In addition, the problem of preventing the growth of algae in bodies of water recently has publicly been taken account of, and therefore there is a tendency to limit the use of phosphates in detergents, but the fluidity and caking preventability of such detergents is inclined to be worse. Accordingly, the need for improvement of properties of granular detergents has become more important.
In this regard, U.S. Pat. No. 2,648,609 and U.S. Pat. No. 3,117,027 have each disclosed a method of forming a film, which is to act as a protective coating, onto the surfaces of detergent particles by means of coating while putting the detergent particles in a fluid state.
In fact these patents are concerned with methods and apparatus aiming at uniform coating, but there still remains a great number of unsolved problems, such as, the coating is liable to be irregular; much aggregation takes place between particles; particles adhere to wall surfaces; the methods are not suitable for mass production; and the like. Therefore, those methods and apparatus are not fully satisfactory.
The term "caking preventability" herein means the ability of the detergent particles not to adhere to each other under high temperature and high humidity conditions and not to become caked, and the term "fluidity" means that the angle of repose of detergent particles, in other words the dischargability of detergent particles out of the storage silo.